In recent years, there has been developed a technology of forming a predetermined pattern on a substrate by scanning electron beams. However, it is time consuming to form a pattern by scanning the electron beams. Thus, it is desired that a predetermined pattern is formed onto a substrate at once at the same magnification with the use of electron beams.
Presently, there are various proposals of electron beam exposure apparatuses for forming a predetermined pattern onto a substrate at once at the same magnification and electron sources used in such electron beam exposure apparatuses (see, for example, patent documents 1 through 6).
Patent documents 1 and 2 disclose an electron beam source 200 as shown in FIG. 23. The electron beam source 200 has an electron passage layer 204 formed on a surface electrode 202. The electron passage layer 204 has plural semiconductor nanocrystals 206 of nanometer-scale. An oxide film 208 is formed on the surface of each semiconductor nanocrystal 206. The thickness of the oxide film 208 is smaller than the crystal grain size of the semiconductor nanocrystals 206. Electrons are emitted from a surface 202a of the electron beam source 200. Thus, the surface 202a of the electron beam source 200 acts as an electron emitting surface.
In patent documents 1 and 2, in a state where the electron beam source 200 is disposed in a vacuum space, electrons e are accelerated by an intense electric field in the electron passage layer 204 including the semiconductor nanocrystals 206. Then, the kinetic energy of the electrons e increases near the surface 202a of the surface electrode 202. The electrons e acquire energy exceeding that of an electrical barrier that restricts the motion of the electrons. Subsequently, the electron beam source 200 emits the electrons into the vacuum space.
Patent document 3 discloses a nitride semiconductor resonance tunnel electron emitting element including a multiple barrier layer constituted by an insulating substrate having formed thereon an AlN layer or an AlGaN layer (where Al(x)Ga(1−x)N and x>0.3) having a thickness greater than or equal to one atomic layer and less than or equal to 10 atomic layers, and a GaN layer having a thickness greater than or equal to five atomic layers and less than or equal to 50 atomic layers.
Patent document 4 discloses an electron beam source including plural electron emitting sources formed on a base; a patterning electrode, which includes a top end formed so as to protrude toward one of the electron emitting sources and also includes an opening through which electron beams can pass; and moving means for moving the relative positions of the base having the electron emission sources formed thereon and the patterning electrode.
Patent document 5 discloses a quantized electron beam generator including an n+ type InP substrate having formed thereon an n+ type InGaAs layer including silicon having a density of 1×1019/cm3, an AlAs0.56Sb0.44 layer, and an In0.53Ga0.47as layer. An insulating isolation region is formed around a plane rectangular region, from the In0.53Ga0.47as layer into the upper part of the n+ type InGaAs layer. The AlAs0.56Sb0.44 layer, which is the rectangular region surrounded by the isolation region, serves as a potential barrier layer. The In0.53Ga0.47as layer above the AlAs0.56Sb0.44 layer serves as a potential well layer. Donut-shaped electrodes exposing the potential well layer are disposed with intervals of 1 μm through 2 μm on the In0.53Ga0.47as layer. By applying a voltage in between these donut-shaped electrodes and electrodes provided on the bottom surface of the n+ type InP substrate, an electric field is generated on the potential well.
Patent document 6 discloses an electron beam source including a bulk region, a barrier region adjacent to the bulk region and having a higher potential than the bulk region, a well region adjacent to the barrier region and having a lower potential than the barrier region, and electric field applying means to apply an electric field on a space adjacent to the well region for causing the potential of the space to incline. The barrier region and the well region are formed to have thicknesses such that the electrons in the bulk region have a maximum transmittance of 100% when permeating the barrier region and the space.    Patent Document 1: Japanese Laid-Open Patent Application No. 2005-317657    Patent Document 2: Japanese Laid-Open Patent Application No. 2006-40725    Patent Document 3: Japanese Laid-Open Patent Application No. 2006-147518    Patent Document 4: Japanese Laid-Open Patent Application No. H7-296755    Patent Document 5: Japanese Laid-Open Patent Application No. H5-74333    Patent Document 6: Japanese Laid-Open Patent Application No. H10-79222